A known valve timing control device adapted to change an opening/closing timing of an intake valve or an exhaust valve in response to a driving condition of an internal combustion engine is attached to one end of a camshaft.
The valve timing control device disclosed in, for example, JPH09-151711A is a vane type control device adapted to an internal combustion engine, which transmits an engine torque from a crankshaft to a camshaft by means of a torque transmitting means such as a timing belt or a timing chain. Further, a rotor, to which plural vanes extending in a radial direction, is fixed to the camshaft, and a timing pulley is coaxially fitted to the rotor so as to form plural hydraulic pressure chambers therein roundly, and each vane is inserted into each hydraulic pressure chamber so as to function as a piston.
In this configuration, a valve timing control device is executed by changing a relative phase between the camshaft and the timing pulley by applying hydraulic pressure for an advancing angle or hydraulic pressure for a retarding angle into a first hydraulic pressure chamber or a second hydraulic pressure chamber of the hydraulic pressure chambers, the hydraulic pressure chambers being divided into the first hydraulic pressure chamber and the second hydraulic pressure chamber by means of the vane.
Specifically, the valve timing control device includes a rotor (17) having plural vanes (18) extending in a radial direction and a housing member (19) in which the rotor (17) is provided. Between the rotor (17) and the housing member (19), hydraulic pressure chambers, arranged so as to be in a round shape, are formed, and each vane (18) is positioned in each hydraulic pressure chamber, and fluid for the advancing angle and for the retarding angle flows therein.
A fluid passage including a main passage (27) extending in an axial direction of the camshaft and a branch passage (13) extending in a radial direction from the main passage (27) is provided at one of a first hydraulic pressure chamber (30) and a second hydraulic pressure chamber (31) formed by dividing the hydraulic pressure chamber by means of each vane (18), and the fluid is introduced through the fluid passage. Because the fluid is introduced through the branch passage (13) simultaneously and evenly into the each hydraulic pressure chamber, responsiveness and smoothness of the operation of the valve timing control has been improved.
Generally, when an engine speed is low, the amount of the hydraulic oil is low. Therefore, pressure applied to the hydraulic pressure chambers is small.
Thus, in order to secure a necessary rotation force, more hydraulic pressure chambers are needed. For example, at the valve timing control device, six chambers are provided. On the other hand, when the engine speed is high, the amount of the hydraulic oil is high. Therefore, rotation force at each chamber is relatively large. Thus, even when the number of the hydraulic pressure chambers is small, a necessary torque for the valve timing control operation can be obtained. However, when the rotation speed of the engine is high, the rotation speed of the camshaft is also high. Therefore, the operation speed of the valve timing control needs to be increased so as to be higher than that in the low rotation speed.
A need thus exists to provide a technology by which the drive torque of the valve timing control device is secured under a condition where the speed of the internal combustion engine is low, and where the amount of the supplied hydraulic oil is low. At the same time, the response speed of the valve timing control device is improved under a condition where the speed of the internal combustion engine is high, and where the amount of the supplied hydraulic oil is high.